Nickel complexes bearing [N,N] 2-pyridylbenzamidine ligands: Syntheses, characterizations, and catalytic properties for ethylene oligomerization

A series of nickel(II) complexes with different steric and electronic substituted 2-pyridylbenzamidine ligands, [2,6-iPr2C6H3–NC(R1)–NH–(5-R3, 6-R2)Py]NiBr2 (R1 = Ph, R2 = H, R3 = H, 1; R1 = Ph, R2 = H, R3 = NO2, 2; R1 = 4-CH3OC6H4, R2 = H, R3 = H, 3; R1 = 4-CH3C6H4, R2 = Me, R3 = H, 4), have been synthesized in high yield and the solid state structures of 1, 2 and 4 have been crystallographically characterized. Activated with methyaluminoxane (MAO), 1–4 showed moderate turnover frequency (TOF) for ethylene oligomerization in dichloromethane. The influences of the ligand structure on catalytic properties were studied. Complex 2 with an electron-withdrawing group revealed the highest TOF of up to 11.7 × 103 mol ethylene/(mol Ni h). Moreover, the reaction temperature and Al/Ni molar ratio were also examined in detail.

Graphical abstractFour 2-pyridylbenzamidine nickel complexes were synthesized and characterized. These nickel complexes showed moderate activities for ethylene oligomerization after activated with MAO. The solvent played an important role on catalytic products. In toluene, ethylene oligomers, alkylated toluene and ditolylmethanes were detected, while only ethylene oligomers were found in dichloromethane.Figure optionsDownload full-size imageDownload as PowerPoint slide